This invention relates to a method of displaying a color image based on image information in the form of electrical signals and a display panel for use in the method of the invention. The display panel has a transparent color pattern layer divided into pixel areas and a recording layer which exhibits reversible changes in transmittance by external stimulus.
For displaying the outputs of computers, facsimiles, scanners, etc., it is common to use an electrically driven display apparatus such as CRTs, liquid crystal displays, plasma displays and LED displays. A common advantage of these displays is that they require no mechanically movable parts. However, these displays are not well suited for displaying still images for long hours, and these displays become very costly when the screen size is enlarged.
There are some proposals for displaying images on a photosensitive or dielectric sheet in the form of a belt by the selective application of a coloring substance such as a powder toner to the photosensitive or dielectric sheet. By this method it will be relatively easy to produce wide-screen display apparatus or to display still images. However, there are several problems with the method incorporating a photo-sensitive or dielectric sheet such as the high cost of processing the photosensitive belt, the unstable running of the belt, the insufficient durability of the belt, and the difficulty in displaying color images and darkness of the display screen.
In addition, there are proposals for a display apparatus using a magnetic coloring substance in the pixels to display images by selective inversion or migration of the magnetic substance. However, such an apparatus is not suited for the display of color images and also suffers from a dark screen.
JP 59-229578 A shows a different method for displaying color images. The method uses an insulating sheet, in the form of a belt, as the display screen base. In addition, three sets of pixels in three different colors, such as red, green and blue, are formed on the insulating sheet so as to make a color pattern such as a mosaic pattern or a striped pattern. Each pixel is provided with an electrode. While the display screen is moved, a voltage is selectively applied between the electrodes in the pixels and a number of needle-like electrodes fixed opposite to the display screen in order to electrically charge selected pixels. Then the charged pixels are hidden by a toner, so that the unhidden pixels form a color image.
The method of JP 59-229578 A has several problems. It entails high cost and it is difficult to form the pixels having electrodes. It is not easy to realize accurate alignment of the pixels in the moving display screen and the fixed needle-like electrodes. The display screen in the form of a belt is liable to deteriorate or become dusty by repeated driving. The adhesion of toner to the pixels is unfavorable for color reproducibility and durability of the display screen.
JP 64-33536 A shows an electrochromic display apparatus having an electrochromic display layer, a set of electrodes to selectively heat the pixel areas of the electrochromic layer and another set of electrodes to selectively apply a voltage to the pixel areas to cause coloration or vanishing. This apparatus also has disadvantages such as the high cost of implementing two electrodes for the individual pixels, complications associated with the control of coloration and banishing, the questions about reliability, the difficulty in reducing the individual pixel sizes for high resolution image reproduction, the low contrast of the displayed images and the inability to display image properly at night or at dark locations.
JP 2-28625 A shows a thermochromic display apparatus having a thermochromic display layer, a thermal head for selectively heating pixel areas of the thermochromic layer to cause coloration and a cooling element for vanishing. This apparatus becomes very costly mainly due to the inclusion of a cooling element and a driving circuit for the cooling element. In addition the apparatus will not properly reproduce color, and contrast of the displayed images and the ability to display images under dark conditions will be poor.